A multi-scaled, transdisciplinary study on the impacts and management of Prosopis, one of the world’s worst woody invasive plant taxa

Thesis (PhD)--Stellenbosch University, 2016.ENGLISH ABSTRACT: Biological invasions are a growing threat to humans and the environment globally and are a substantial problem in South Africa. The tree genus Prosopis is a prominent invasive in South Africa and globally. This study explores the global biogeography, costs and benefits of the genus, the conflicts of interest regarding its management and use, and the options available for management. The ecological costs of the genus, as well as social costs and benefits, are explored further using South African case studies. Perceptions of the tree and its relative use compared to native trees were also assessed across multiple stakeholder groups. This provided evidence that is needed to formulate integrated management plans. Different barriers to effective management of Prosopis in South Africa perceived by multiple stakeholders were assessed, and strategic and prioritisation plans were developed to guide improved management. The methods included literature reviews, vegetation surveys, questionnaires and workshops. Various Prosopis taxa have been introduced into over 100 countries, and areas that are currently not invaded but which have a high risk of being invaded were identified using bioclimatic modelling. Numerous detrimental effects on biodiversity, ecosystem services, human health and livelihoods and economies were identified. Vegetation surveys showed that Prosopis is having a major impact on native plant biodiversity across South Africa. Increased density of Prosopis invasions leads to decreased native tree species richness and abundance and reduced cover of perennial shrubs and grasses. Prosopis is also reducing population stability through reduced recruitment and increased mortality of native trees. Reductions in the supply of water and natural grazing, roots breaking infrastructure and reductions in property value were costs identified in social surveys. Prosopis also provides benefits including fodder, shade and fuelwood, however, the majority of all stakeholders viewed it to have higher costs. In addition, the household use of Prosopis is lower than that of native trees, suggesting that native trees (which are displaced by Prosopis), are still more important for households. More than 90 % of respondents would like to see a decrease in Prosopis population densities. However, many barriers relating to the control of Prosopis exist – including: lack of knowledge, lack of funding, conflicts of interest, and institutional issues such as poor communication and cooperation, mismanagement, and poor prioritisation and strategic planning. Farmers and Working for Water managers raised markedly different barriers showing differences in world views. A management strategy for Prosopis was developed. It outlines different control options and details an approach for the co-ordination and monitoring of projects. It was stressed that improved biological control is needed, as is improved management on private land. The controversial “control through utilisation” approach needs further research to assess its feasibility. Management approaches (prevention, eradication, containment and asset protection) were assigned to individual municipalities go guide management. Multi-criteria decision making analysis (using Analytic Hierarchy Process) was used to identify and prioritise assets for protection at various scales. An integrated managed approach, in particular the use of biological control along with other methods was identified as key for successful managed in the future. Using transdisciplinary approaches, this thesis provided insights on the effects of Prosopis invasions in South Africa, and provided objective support for improved management. Drawing on case studies conducted in the thesis and other published material, a framework for a national strategy to guide the management of this problematic invasive tree in South Africa was produced.AFRIKAANSE OPSOMMING: Die teenwoordigheid van biologiese indringers is 'n groeiende bedreiging vir die mens en die omgewing wêreldwyd en is 'n beduidende probleem in Suid-Afrika. Die boom genus Prosopis is 'n prominente indringer in Suid-Afrika en in die wêreld. Hierdie studie ondersoek die globale biogeografie, koste en voordele van die genus, die botsende belange met betrekking tot die bestuur en gebruike, en die opsies wat beskikbaar is vir die bestuur daarvan. Die ekologiese koste van die genus, sowel as die sosiale impakte en voordele, word ondersoek met behulp van Suid-Afrikaanse gevallestudies. Persepsies van die boom en sy relatiewe gebruike, in vergelyking met inheemse bome, is deur verskeie belangegroepe geassesseer. Dit verskaf bewyse vir die formulering van geïntegreerde bestuursplanne. Verskillende hindernisse tot effektiewe bestuur van Prosopis is in Suid-Afrika deur verskeie belanghebbendesgeïdentifiseer en geprioritiseer. Strategiese planne vir verbeterde bestuur is ontwikkel. Die studie metodes sluit literatuurstudie, plantegroei opnames, vraelyste en werkswinkels in. Verskeie Prosopis spesies is in meer as 100 lande ingevoer. Gebiede waar Prosopis nie tans as indringer geïdentifiseer is nie, maar waar 'n hoë risiko bestaan, is met behulp van bioklimatiese modellering geïdentifiseer. Talle nadelige impakte op biodiversiteit, ekosistemiese dienste, menslike gesondheid en voortbestaan asook ekonomieë is geïdentifiseer. Plantegroei opnames het getoon dat Prosopis 'n grootskaalse impak op inheemse plant biodiversiteit in Suid-Afrika het. Verhoogde digtheid van indringende Prosopis bome lei tot ʼn afname van inheemse boomspesies, meerjarige struike en grasse. Prosopis beïnvloed ook ekosisteem stabiliteit as gevolg van verhoogde mortaliteit van belangrike inheemse bome. Sosiale opnames het aangedui dat verminderde water voorsiening, afnames van natuurlike weiding, wortels wat infrastrukture beskadig en verlaging in die waarde van eiendomme teweeg gebring word. Prosopis bied ook voordele soos voer, skaduwee en brandhout, maar die meerderheid van belanghebbendes beskou die nadelige impakte as belangriker as die voordele. Daarbenewens is die huishoudelike gebruik van Prosopis minder prominent as die van inheemse bome, en is inheemse bome belangriker vir huishoudings. Meer as 90% van die respondente wil graag 'n afname in die Prosopis bevolkingsdigthede sien. Daar is verskeie hindernisse vir die beheer van Prosopis, insluitende: 'n gebrek aan kennis, gebrekkige befondsing, ʼn konflik van belange, institusionele kwessies soos swak kommunikasie en samewerking, wanbestuur, swak prioritisering en gebrek aan strategiese beplanning. Boere en bestuurders van Werk-vir-Water, identifiseer onderskeidelik verskillende hindernisse wat dui opverskillende wêreldbeskouings. ʼn Bestuurstrategie vir Prosopis is ontwikkel. Die strategie stel verskillende kontrole-opsies voor en 'n benadering vir die koördinering en monitering van projekte. Dit beklemtoon dat verbeterde biologiese beheer en bestuur van private grond benodig word. Die omstrede "beheer deur gebruik" benadering moet verder nagevors word om die haalbaarheid daarvan te bepaal. Bestuursbenaderings (voorkoming, uitwissing, beheer en bate beskerming) is aan individuele munisipaliteite gegee om leiding aan bestuur te gee. Multi-kriteria besluitnemings analises (met behulp van “Analytical Hierarchy Process”) is gebruik om bates te identifiseer en te prioritiseer vir bestuur op verskillende vlakke. 'n Geïntegreerde bestuursbenadering, wat in die besonder die gebruik van biologiese beheer saam met ander metodes voorstel, is geïdentifiseer as die sleutel tot suksesvolle bestuur in die toekoms. Hierdie tesis verskaf insigte oor die gevolge van Prosopis indringing in Suid-Afrika, deur middel van transdissiplinêre benaderings, en verskaf objektiewe ondersteuning van die bestuursbehoefte. Danksy gevallestudies in die proefskrif en ander gepubliseerde materiaal, is 'n raamwerk vir 'n nasionale bestuurstrategie van hierdie problematiese indringer boom in Suid-Afrika daargestel